The invention relates to a hot-gas reciprocating machine, comprising a plurality of working spaces, the volumes of which can be varied at a phase difference with respect to each other by pistons which are coupled to a crank shaft. A working medium in each of the working spaces performs a thermodynamic cycle during operation; each of the working spaces is connected, via an associated connection duct including a non-return valve which opens in the direction of the relevant working space, to a main supply duct for working medium in which a closing member is provided, the main supply duct being connected to a source of pressurized working medium. A hot-gas reciprocating machine of the kind set forth is known from U.S. Pat. No. 3,546,877.
Within the scope of the present application, hot-gas reciprocating machines are to be understood to mean hot-gas reciprocating engines, cold-gas refrigerators and heat pumps. In each of these machines the working medium in the working space is alternately compressed when it is mainly present in a sub-space, the compression space, is subsequently transported, via a regenerator, to a further subspace, the expansion space, after which, when the working medium is mainly present in the expansion space, it is expanded, and finally it is returned, via the regenerator, to the compression space to complete the cycle. The compression space and the expansion space have different mean temperatures with respect to each other during operation. The pistons which vary the volumes of the different working spaces are coupled to the crank shaft at a different crank angle with respect to each other. Consequently, a phase difference exists as regards the volume variation and the pressure variation occurring in each working space.
The power of the machine can be increased by increasing the quantity of working medium in the various working spaces of the machine. Notably, in hot-gas reciprocating engines for traction purposes, particularly at low speeds and powers, when a sudden power increase is desired, for example, in the case of acceleration, it is advantageous to supply working medium to each of the working spaces at the instant at which the working medium participating in the thermodynamic cycle in the relevant working space reaches substantially the highest pressure occurring during the cycle. This is because the highest pressure of the working medium then increases, so that the supplied working medium directly participates in the expansion without the engine first having to perform work of compression on the added working medium. In this way we prevent the engine torque from being initially decreased, (a braking effect). Consequently, when the supply of working medium takes place at maximum cycle pressure, the engine immediately delivers a higher power.
The supply of working medium to the sole working space of a hot-gas reciprocating machine exclusively during the period in which the maximum cycle pressure occurs in the said working space, is known from U.S. Pat. No. 2,616,244. Therein, a valve which is mechanically controlled by the machine is periodically opened, with the result that the working space is periodically brought in open communication with the working medium source. A construction of this kind is unattractive for the present machine comprising a plurality of working spaces, because of the fact that a large number of valves is required, each of which is to be opened at an individual instant, because in the thermodynamic cycles the maximum pressure occurs at mutually different instants.
The supply of working medium exclusively at maximum cycle pressure also involves a drawback. In order to enable working medium to be continuously supplied to the working space at the ever increasing maximum cycle pressure during the periodic supply, the working medium in the source should be under a very high pressure. This means that the commonly used compressor of the power control system must have a very high compression rate. An expensive compressor of high power is thus required.